Weißbauchtölpel vs Maskentölpel

Kurz gesagt

The most reliable field mark between Brown Booby and Masked Booby is the overall body and underpart contrast: adult Brown Booby shows a sharp division between dark brown upperparts and a clean white belly, while Masked Booby adults are bright white overall with only the wings and tail dark. Juvenile patterns differ: young Brown Boobies are dusky above with brown-flecked underparts, whereas juvenile Masked Boobies are mottled brown above with a white collar and mostly white underparts. Structure also helps: Masked is bulkier, with a longer, yellowish bill and longer wings. In flight, note the Brown Booby’s shorter wings and more compact jizz compared to the Masked Booby’s long, slender wings and pointed tail.

Bestimmungstipps

1. Adult underpart contrast: Brown Booby adults always show a sharp division between dark brown upperparts and a clean white belly; Masked Booby adults are almost entirely white below, with only the wings and tail dark. This is the single best mark at most ages.
2. Juvenile/immature pattern: Juvenile Brown Booby is brownish above with brown-flecked white underparts and lacks a white collar; juvenile Masked Booby is mottled brown above with a clear white collar and mostly white underparts. Look for the collar on Masked Booby immatures.
3. Head and facial pattern: Adult Masked Booby has a distinctive black or blue-black mask of bare skin around the face, contrasting with the white head. Brown Booby’s head is dark brown, blending into the upperparts, with no mask effect.
4. Bill color and shape: Masked Booby has a long, pointed, yellowish bill that is longer than the head and slightly downcurved; Brown Booby’s bill is sharp but less elongated, and bare part color varies by sex (blue orbital ring in males, yellow in females).
5. Wing and tail structure: Masked Booby is larger and more elongated, with long, slender wings and a pointed tail; Brown Booby is more compact, with shorter wings and a long, tapered tail but less pronounced than Masked.
6. Flight jizz: Brown Booby flaps faster and appears more compact in flight, often low over inshore waters. Masked Booby glides more, with slower, deeper wingbeats and a more elongated silhouette.
7. Underwing pattern: Masked Booby’s underwing is white with dark flight feathers, creating a sharp contrast; Brown Booby’s underwing is less sharply patterned, generally dark above and white below but without the crisp division.
8. Sexual dimorphism: Brown Booby shows sexual differences in bare part color (orbital ring), but plumage is similar; Masked Booby sexes are similar in plumage and bare parts.
9. Habitat context: If seen close to shore or over inshore waters, Brown Booby is more likely; Masked Booby is more often found farther offshore.
10. Colony behavior: Masked Booby is highly territorial at colonies with elaborate displays; Brown Booby is also colonial but less aggressive in display.
11. Size impression: Masked Booby is noticeably larger and heavier, but this can be hard to judge without direct comparison.
12. Voice: Not usually helpful; both are silent at sea, with Masked Booby only vocal at colonies.
13. Pitfalls: Immature Masked Booby can appear brownish above, but the white collar and whiter underparts help separate it from the more uniformly brownish juvenile Brown Booby.
14. Bare part color: If seen well, Masked Booby’s yellowish bill and black/blue-black facial skin are distinctive; Brown Booby’s bare part color varies by sex and is less striking.
15. Age progression: Masked Booby immatures gradually acquire more white on the head and rump, reaching full adult plumage by about three years; Brown Booby juveniles already resemble adults but are duller and browner overall.

Größe

Masked Booby is the larger of the two, with a length of 75–85 cm and a wingspan of 160–170 cm, compared to Brown Booby’s 75–80 cm length and up to 150 cm wingspan. Masked Booby is also heavier (up to 2.2 kg vs. Brown Booby’s typical 1.3 kg maximum). Brown Booby appears more compact and less elongated in the field, with relatively shorter wings and tail.

Gefieder

• Juvenile/immature: Juvenile Brown Booby is grey-brown above with darker head and upperwings, and underparts heavily flecked brown on white, lacking a clean white collar. Juvenile Masked Booby is mottled or streaked grey-brown above with a distinctive whitish neck collar, dark brown wings, and white underparts. Older Masked Booby immatures show increasing white on the head and a broader white collar and rump, reaching full adult white head by 14–15 months.

• Adult: Brown Booby adults have dark brown to blackish head, neck, and upperparts, with a sharply contrasting white belly and lower breast. Masked Booby adults are bright white overall except for the dark wings and tail, with a black or blue-black facial mask and bare skin. The underwing of Masked Booby is white except for the dark flight feathers, while Brown Booby’s underwing is less sharply patterned but generally dark above and white below.

• Bare parts: Brown Booby males have a blue orbital ring, females yellow; Masked Booby shows black or blue-black bare skin around the face and a long yellowish bill. Brown Booby’s bill is sharp and jagged-edged, but less strikingly colored.

Verhalten

Both species are gregarious and often forage in groups, but Brown Booby is more commonly seen commuting and foraging at low height over inshore waters, often closer to land. Masked Booby tends to forage farther offshore and is highly territorial at nesting colonies, with elaborate displays such as sky-pointing and headshaking. In flight, Brown Booby flaps faster with shorter wings, while Masked Booby glides more on its long, slender wings.

Lebensraum

Brown Booby is more likely to be seen nearshore, over inshore waters, and sometimes even close to land. Masked Booby prefers more pelagic, offshore waters and is less frequently seen near the coast except at breeding sites. Both nest on islands, but Brown Booby is more likely to be encountered by coastal observers.

Stimme

Both species are mostly silent at sea. Brown Booby may occasionally grunt or quack, but this is rarely heard in the field. Masked Booby is also silent at sea but can be noisy at colonies, with males giving descending whistles and females loud honks. Voice is not a reliable field mark for separation at sea or in flight.